Coupling arrangement for amplifiers and repeaters



y '2 1939- w.- VAN B. ROBERTS 2,159,944

COUPLING ARRANGEMENT FOR AMPLIFIERS AND REPEATERS Filed Sept. 2, 1926 129:1 12;. 2 12g .55 Fly 4 'INVENTOR.

wmea VAN a ROBERTS" ATTQRNEY Patented May23, 1939 i UNITED STATES PATENT OFFICE j con rmNc ARRANGEMENT FOR mums AND nsrna'raas Walter van B. Roberts, Bronxville, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application September a, 1926, Serial, No. 133,283 3 Claims. (01. 178-44) The invention relates to couplings through In connection with Figelement Shows a which a large range of frequencies are ordinarily resistance where the mutual impedance is simply used. It relates more particularly to radio freequal to the resistance and hence is practically quency amplifiers, but is not limited to the exact independent of frequency. In other words, the

range of frequencies which are ordinarily undercoupling values are constant regardless of the 5 stood to be included in the radio frequency range. change in frequency. It might be also applicable to audio frequencies land 3 of Fig. 2 show inter-coupled inductance or even lower. coils. The terminals at the left may be connected It has been known in connection with ordinary to one circuit and the terminals at the right in coupling arrangements heretofore used which inare connected to another circuit in a similar way 1 tercouple difi'erent elements of energy changing as Fig. 1 may be connected. In this type of couarrangements such as amplifiers, detectors, etc. pling, as explained before, the mutual impedance used with oscillatory currents, that the particular between these two circuits varies directly with couplings were always susceptible and responsive the frequency so that with an increase of freto one particular frequency which predominated quency an increase of coupling exists. Also dif-q 1 over all of the others. This was due to the inflculties arise from the fact that there are other herent characteristics of the coupling elements, elements entering into the system, such as disparticularly the relation between the capacity tributed capacity which causes the curve defining.

and the inductance of the circuits. a mutual inductance throughout a given range to In a great many cases throughout the radio of frequencies to deviate from a straight line. and electrical art there is a necessity for coupling 4 in Fig. 3 is a condenser used for coupling between two or more circuits. These circuits are between two circuits. This type of coupling said to be coupled when an alternating current works just the opposite from the type shown in flowing in one produces an electromotive force Fig. 2; that is, the mutual impedance, due to a in the other. The number of volts of electromocondenser common to both circuits, increases di- 5 tive force produced in either circuit per ampere rectly as the wave length or varies as the rein the other circuit is called the mutual imciprocal of the frequency.

pedance between the two circuits. This mutual 5 in Fig. 4 shows a single inductance coil and impedance may be obtained in several different is substantially the same type of coupling as is ways. shown in Fig. 2, inasmuch as the magnitude of If the two circuits are coupled by means of a the mutual impedance varies directly as the fremutual inductance, sometimes called a transquency. This is what is commonly known as former,.the mutual impedance increases directly the auto-transformer arrangement. with the req en I m y cases it is desir- 6, 'l and 8 of Fig. 5 show respectively a capacity able that the mutual impedance between the shunted by aninductance coil which is coupled rc its be independent of frequency or that it to another inductance coll. This t pe of cony w h e u n y s ap h w th the pling can be made approximately equivalent to ordinary case of the mutual inductances. the type shown in Fig. 3 over moderate ranges The objects of this invention. are to obtain of frequency, as the transformer is so designed means for controlling the variation of mutual with respect to the capacity as to make the 4 mp n e. I m y be controlled in such a way mutual impedance vary inversely with the frethat it will be made to vary in any desired manquency over the desired range of frequencies;

her w th t e eq e ye ma or do Now, in many cases it is desirable that the this and other objects, some of which will be. mutual impedances between two circuits be infound to be obvious from, and are explained more dependent of frequency, or that it vary with fre- 5 precisely in connection with the annexed drawquency less rapidly than in Figs. 2, 3, 4 and 5. ing and the specification. It is usually impractical to use resistance cou- In this drawing Fig. lshows a resistance coupling for this purpose as 'it introduces energy pling; losses which are undesirable. My invention con- F ShOWS e t fiinductance (101111111182 sists in the method of utilizing both inductive 50 Fig. 3 shows a capacitance coupling; and capacitive coupling at the same time so that Fig. 4 shows-a self-inductance coupling; as the mutual impedance of one element de- Fig. 5 shows modification of Fig. 3 and creases that of the other element increases and Figs. 6 to 11 inclusive show modifications and vice-versa. By proper choice of the relative magadaptations of the improved coupling means. ld s 0f t e WO 0 9 8 means, the o a 55 mutual impedance may be made to stay as nearly constant as there is any need for over a range of frequencies, such as is used in what is com; monly known as the broadcast range or that range of frequencies commonly used between 200 and 600 meters.

If desired, the relative values of the two coupling means maybe designed so that the total mutual impedance increases somewhat, with the frequency, but not so rapidly as the mutual impedance due to the simple inductive coupling. Fig. 6 shows, in the simplest form, this type of compound coupling in which I0 and I l are mutual inductances connected through a common capacity 9. The intercoupled circuits maybe connected to the right and left hand terminals re spectively, as before. It is essential thatthe' windings l0 and H be in opposite directions so: that the voltages produced by the inductive a'nd capacitive couplings add to each other rather than to subtract from each other, which would be the caseif an attempt was made to combine the arrangements shown in Figs. 3 and 4, make a coupling element consisting of a coil in series with a condenser. However, this last mentioned coupling combination is useful in wave traps and. filters where it is desired .that the mutual impedance vanish completely forv some particular frequency.

Fig. 7 shows a method equivale t to Fig. 6, but having what is in some cases the advantage of no metallic interconnection between the coupled circuits. Here l2 and i3 represent intercoupled inductances and I6 and F5 are separate inductances coupled in the same way with the exception that condenser 33 is shunted around the element i5. 1

Fig. 7 is the combination of Figs. 2 and 5. When the capacity is only indirectly connected by means of a transformer in one of the circuits, the polarity of this transformer may be reversed so that a single coil can be used, as shown in Fig. 8. This is probably not so desirableas the arrangement shown in Fig. 6 and the only advantage it has is that the paths for direct current are nowhere interrupted, as theywould be by the condenser 9 in Fig. 6. In this last figure the capacity I6 is shunted by an inductance which is coupled with the inductance I1. These two inductances must be arranged in the same way as it and I i of Fig. 6. I8 is the common mutual inductance which is the equivalent to the inter-coupled inductances l2 and it of Fig. 7. i

In Fig. 9 this arrangement is adapted for use with an antenna and I9 and 2! are inter-coupled inductances as in Fig. 6 and 26 is a capacity which is mutual to both circuits. At ,present several taps are usually provided on thefantenna coil of receiving sets and it is quite noticeable that the tap which works best at short waves is not the best one for long waves. The arrangement of Fig. 9 allows the use of the same tap for all wave lengths without noticeable difi'erence in efiiciency. Similarly in making radio frequency transformers to go between vacuum tubes, it is well known that a simple primary coil, having the best number of windings for amplification at the middle of the wave length range, will have too few turns for the best results at one end of the range and 'too many turns for maximum results at the other end of the range.

Fig. 10 shows the arrangement in Fig: 7 adapted to this purpose, but other arrangements are equally possible, such as Fig. 6. Here 22 and 23 are inter-coupled inductances and 25 is an inductance which is coupled to its primary which is quency filters.

coils are coalesced with clusion and nature of as the output load or terminating resistance.

if in Fig; 9 or 10 thev shunted by'the condenser 26-. These inductances together with inductance 24 and capacity 21 make up the tuning arrangement for the grid of the input connections for the instrument desired to be coupled.

Still another use for compound coupling is in connection with continuously tunable radio fre- The width of the band of frequencies passed by a simple filter depends upon the mutual reactance between sections so that as it is desired to select a band of frequencies some 10 kilocycles wide notmatter what part of the spectrum of broadcast frequencies we are selecting from, it is desired to have a mutual impedance element whose value does not vary appreciably over the broadcast range. Fig. 11 shows a typical filter section using this type of coupling. This is an adaptation of the coupling arrangement shown in Fig. 6, where the transformer the rest of the inductances. Here 28 and 3| are adjustable condensers. one in each' side of the two circuits. 29 and 30 are inductances associated as in Fig. 6 and 32 is the mutual capacity.

A source of radio frequency voltage E is conventionally shown connected across the input terminals of the filter, the source being a signal energy collecting means, or a preceding amplifier of ,collectedsignal energy, as is well known to those skilled in the prior art. Across the output terminals of the filter is connected a load conventionally represented equal to the value of terininating resistances. This load has a resistance value correct for ensuring the proper uniform band pass selecting characteristic of the filter. The selected currents flowing through the load may be utilized to operate translating devices in any of the usual ways well known to those skilled in the artof radio reception. The term filter, as used heretofore, is understood to imply to those skilled in the art, the'mathematical relations between the filter element and, additionally, the inthe voltage source, as well It will be understood that resistances of the coils vary with frequency, as is usually the case, the compound coupling will not be designed for constant mutual impedance but will be so proportioned that the total mutual impedance increases with frequency to the extent desirable to keep pace with the increase of resistance. The values of resistances in two coupled circuits always determine theoptimum values of the mutual impedance between the circuits. Care should' 'th'erefore be taken to prevent unnecessary effective resistances at any particular frequency.

While only one application has been specifically features disclosed be used in the coupling of audio plifiers as well as by the above not desired that this invention Having described my invention with the various modifications, I wish to be limited only by the scope of the following claims and not by the exact structure disclosed,

What; wish to claim is: 1. A compound coupling arrangement for providing an effective mutual impedance between twdcircuits that varies with frequency over a range of frequencies in a predeterminable manner, comprising mutual inductance between se- 'ductors and adapted ductors arranged in series, each of the secondary inductors being magnetically coupled to an associated one of said primary inductors,a variable e condenser conncted'across the secondary into tune the latter over a given frequency range, one of said primary inductors transmitting high frequencies of said range most efficiently, and the other primary inductor transmitting low frequencies of the range most efliciently.

3. A compound coupling arrangement for coupling two circuits with a total effective mutual impedance that varies with frequency over a relatively wide range of frequencies 'in a predetermined manner comprising in combination a 5 first coupling between said circuits arranged to provide an effective mutual impedance therebetween which increases as frequency increases, a second coupling between said circuits arranged to provide an efiectivemutualimpedance there- 10 between which decreasesfas frequency increases, said second coupling-comprising a series con- /denser in one of said'circuits, a coil shunting said condenser and having sufficientinductance to make the resonant frequency of the combination 15 of said coil and said condenser low compared to any frequency in said range, an inductive element in said other circuit, and mutual inductance between said coil and said element. 20

WALTER vmn. nonnars. 

